Internal static excitation system for a dynamoelectric machine

ABSTRACT

A static excitation system is provided for self-excitation of a large generator with gas and/or liquid cooling systems which is located inside or closely coupled to the generator casing so as to utilize the generator coolant system. The static excitation transformer preferably has one primary winding connected to a supplementary winding in the dynamoelectric machine slots responsive to the generator field flux and another primary winding comprised of the neutral leads of the generator main winding responsive to generator current. The secondary of the internal excitation transformer thus provides a compound voltage source, responsive to both generator field flux and generator current which is then rectified and applied through suitable controls to the generator field.

United States Patent Kudlacik et al.

[54] INTERNAL STATIC EXCITATION SYSTEM FOR A DYNAMOELECTRIC MACHINE [72]Inventors: Henry W. Kudlacik, Schenectady;

David M. Willyoung, Scotia, both of NY.

[73] Assignee: General Electric Company [22] Filed: June 22, 1971 [21]Appl. No.: 155,512

[52] US. Cl. ..322/59, 322/25, 310/52 [51] Int. Cl. ..H02p 9/14 [58]Field of Search ..3l0/52, 58, 53, 65, 54, 64, 310/68, 68 D, 162, 179,180, 184; 322/25,

1s] 3,702,964 [45] Nov. 14, 1972 3,435,326 3/1969 Zechlin ..322/253,132,296 5/ 1964 Nippes ..322/90 3,479,543 11/1969 Drexler ..3 10/1802,920,261 l/ 1960 Braun ..322/25 Primary Examiner-R. SkudyAttorney--William C. Crutcher et a1.

[57] I I ABSTRACT A static excitation system is provided forself-excitation of a large generator with gas and/or liquid coolingsystems which is located inside or closely coupled to the generatorcasing so as to utilize the generator coolant system. The staticexcitation transformer preferably has one primary winding connected to asupplementary winding in the dynamoelectric machine slots responsive tothe generator field flux and another 1 primary winding comprised of theneutral leads of the [56] References Cited generator main windingresponsive to generator current. The secondary of the internalexcitation trans- UNITED STATES PATENTS former thus provides a compoundvoltage source, I responsive to both generator field flux and generator3,254,293 5/1966 Stembruegge ..322/25 current which is then rectifiedand applied through 3,401,328 9/ 1968 Hartung ..322/59 Suitabe controlsto the generator field 2,798,975 7/1957 Akers ..310/64 2,788,456 4/1957Fromm ..310/64 14 Claims, 7 Drawing Figures SUPERVISORY clRcm' l7GENERATOR 3/ A ellilv'lh coouus A TRANSFORMER I SYSTEM JL LE. LE. 24 101.5-1 PRIMARY PRIMARY 1 I H I wmoms WINDING 2 (POTENTIAL) (CURRENT) 2 II In 22 J l I I 230- I 1 i 19 l. r l I I INTERNAL E XCITATION 2m5fi3'3?* GENERATOR I '1 TRANSFORMER T egit-2 i' '1 i I PROTECTIVE I T0RI2 I RELAYING I "a. wmoms L 1 I In 1 SUPPLEMENTARY I 3- EXCITATION Iwmome I l I 7 1 til: ROTOR 2 W I I i 1 8 l I STATOR I I 1 L lPATENTEDuuv 1 4 m2 SHEET 2 OF 5 INVENTORS HENRY W. KUDLACIK, DAVID M.WILLYOUNG, w. 6 6,4

mum

ll'Il-llll THEIR ATTORNEY.

PATENTEUnnv 14 I972 3. 702.964

SHEET 3 [IF 5 50- EXTERNAL m F|G.4 NEUTRAL E;

SCPT EXCITATION F|G 5 CONTROL INVENTORS HENRY W.-KUDLAC|K, DAVID M.WILLYOUNG,

THEIR ATTORNEY.

PATENTED um 14 m2 MmoBm SHEET 5 BF 5 INVENTCQS' HENRY W. KUDLACIK, DAVIDM. WILLYOUNG,

THEIR ATTORNEY.

BACKGROUND OF THE INVENTION This invention relates generally to staticexcitation systems for large gas or liquid cooled dynamoelectricmachines, and more particularly to self-excited dynamoelectric machinesusing excitation transformers to produce a compounded excitation powersource for the field windings. I

Excitation systems for very large dynamoelectric machines such asturbine-generators have grown in complexity and rating along with theratings of the generators themselves. Early excitation systems includedrotating power sources such as a separate DC generator driven by theturbine generator shaft which supplied field excitation through sliprings and brushes to the rotating field winding. Another arrangement inwhich the excitation power source is rotating employs an AC exciterdriven by the turbine-generator with rectification and control of theexcitation voltage in external stationary rectifier banks.

Another variation wherein components of the excitation source arerotating, is the rotating rectifier system, where an AC exciter drivenby the turbine-generator supplies current to the field windings throughrectifiers which are carried on the rotating shaft.

A separate, broad category of excitation systems, and one to which thepresent invention pertains, is the static system where the excitationpower source, the rectifiers and the voltage regulator components arenonrotating. Static excitation power sources have been proposed whichsupply field excitation to a generator by taking excitation power fromthe stator output buses by means of an external excitation transformerwith potential" and current windings coupled with the generator lines.Although such systems, sometimes controlled by a saturating" DC controlwinding on the excitation transformer, provide an excellentself-regulating power source, these systems tend to be large andexpensive, complicate the power plant layout, require separate coolingsystems, and require undesirable connections into or between theisolated phase buses between the generator and the main powertransformer.

Very rapid response and a largely self-regulating excitation action canbe obtained in a static system by compounding the excitation windings,so that the excitation voltage is responsive both to generator outputload current and to main generator terminal voltage. The latter is, inturn, derived. from the rotor-produced synchronous flux (which isdependent upon the rotor field current diminished by the vectoriallysubtracted stator leakage reactance drop (which depends on statorcurrent). Within the limitations imposed by compounding" power drawnfrom terminal voltage and terminal current separated as they are by afixed power factor angle, it is'possible to construct static excitationsystems which exhibit undercompounding, flat compounding, orovercompounding in certain power factor ranges. Typical of such compoundstatic excitation systems are U.S. Pat. No. 2,208,416, Friedlander etal. and US. Pat. No. 2,454,582, Thompson et al. It is characteristic ofsuch static systems that linearity in the self-regulating action extendsonly over a limited range of terminal voltage, terminal current andpower factor operation so that the designer seeks to achieve acompounding condition, which compromises the excitation requirementsover the entire range of operation with minimum total regulating power.

I Varioussuggestions have been made in the prior art concerning theprovision of static sources of excitation power internal to thedynamoelectn'c machine, such as auxiliary windings in the end turnregion (French Pat.

0 No. 1,050,847), or auxiliary windings in the main winding slots (US.Pat. No. 3,132,296 to Nippes). An excitation power source providingcompounding through intemal windings responsive to field flux and tomain winding leakage flux is disclosed in U.S. Pat. No. 3,479,543 toI(.F. Drexler, assigned to the present assignee. Suggestions have alsobeen made for tapping the main winding of a'dynamoelectric machine, asin US. Pat. No. 3,035,222 issued to H.B. Stone, in order to obtain apower source for external rectification, such an arrangement being onlysuitable for relatively small alternators.

It would be desirable to have an excitation system with high response,simple control, compounding which can be adjusted over a wide range tobe either self-regulating or to supply forced excitation tailored to theinstantaneous system requirements, using internal windings, and whichwould be adaptable to integration with modern gas or liquid cooledgenerators in a simple, compact, reliable manner.

Accordingly, one object of the present invention is to provide animproved static internal compounded excitation system which is suitablefor cooled dynamoelectric machines.

Another object of the invention is to provide an improved, compactexcitation transformer which is adapted for placement within thegeneratorcasing or in very close proximity thereto by the use of thegenerator coolants, while providing a compound excitation power source.

Another object is to provide a widely adjustable static, compoundexcitation power source whichv is dielectn'oally isolated from the maingenerator winding and is integrated into the generator neutralconnections rather than being connected to the generator output lines.

DRAWING The subject matter which is regarded as the invention isparticularly pointed out and distinctly claimed in the concludingportion of the specification. The invention, however, both as toorganization and method of practice, together with further objects andadvantages thereof, may best be understood by reference to the followingdescription, taken in connection with accompanying drawing in which:

FIG. 1 is a simplified schematic view of a turbinegenerator with a newform of static excitation system, and an integrated internal neutral andinternal excitation transformer cooled by the dynamoelectric machinecooling system.

FIG. 2 is a fragmentary elevation drawing, partly in section, of theupper end of a dynamoelectric machine illustrating the physicalarrangement of components,

FIG. 3 is a cross section through the stator slot taken along linesIlI-1ll of FIG. 2,

FIG. 4 is a simplified schematic drawing similar to FIG. I butillustrating a modified form of the invention with an external connectedneutral,

FIG. isa simplified schematic drawing illustrating another modificationof the invention with respect to the means of controlling the internalexcitation transformer,

FIG. 6 is a simplified schematic drawing illustrating anothermodification, wherein an external, but adjacent excitation transformerutilizes the dynamoelectric machine cooling system.

FIG. 7 is a simplified schematic drawing illustrating yet anothermodification wherein power to the potential winding of the excitationtransformer is supplied from an auxiliary terminal transformer.

SUMMARY OF THE INVENTION dynamoelectric vmachine. The secondary oroutput winding of the excitation transformer supplies a conventionalrectifier for providing the field excitation power through conventionalslip rings.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1 of thedrawing, a dynamoelectric machine such as a large turbinegenerator isschematically depicted as including a stator 1 and a rotor 2 operatingwithin a sealed enclosure or casing 3. A dynamoelectric machine coolingsystem is depicted symbolically by cooling coils 4 and recirculating fan5 inside the casing 3 connected to an external system 6 for vrejectingheat outside the casing. The foregoing symbolic representation of thecooling system can take a great many forms well known to those skilledin the art for large dynamoelectric machine such as cooling singly or incombination with a gas, such as hydrogen, recirculated by fans mountedon the rotor, or cooling with liquids such as oil or water recirculatedby pumps through tubes among the electrical windings or through passagesin the windings themselves. Exemplary of such systems is US. Pat. No.2,695,368 issued to CE. Kilboume and assigned to the present assignee.

Disposed on the rotor 2 is a field winding 7 supplied through slip ringand brush arrangement 8 from a 3- phase bridge-connected rectifier bank9. Control of the rectifier voltage is afforded by means of siliconcontrolled rectifiers connected in shunt across one side of therectifier bridge output. The rectifier bank 9 and means for controllingit exemplified by silicon controlled rectifiers 10 is typical ofconventional or known excitation control circuits. A number of otherarrangements suitable for excitation control are suggested in US. Pat.No. 3,369,171 issued to L]. Lane and assigned to the present assignee.

Disposed in slots in the generator stator in a conventional manner is agenerator main winding 11 comprising 3-phase windings 11a, 11b, 110.Each phase set,

such as 11a, may in actuality include parallel connected windings, butis illustrated simply as a single winding having a terminal lead 12 anda neutral lead 13. Y

A conventional arrangement for connecting the grounding transformerincorporating suitable protective relaying. However, in the presentpreferred arrangement, only the line leads 12 are brought out of thegenerator casing 3 through bushings 14. The neutral leads 13, on theother hand, comprise single turn primary windings for an internalexcitation transformer indicated schematically by dashed enclosure 15.Although the neutral leads simply make one pass through a laminated coreto form a one-tum primary winding, the primary winding is depictedsymbolically by coils 16 in FIG. 1 suggesting the primary turns. Afterpassing through the core of the internal excitation transformer 15, theneutral leads 13 are connected together at a common neutral connectionpoint 17 which is located inside the generator casing 3 and ohmicallyconnected through a bushing 17a to externally located grounding andprotective relaying equipment 17b of the conventional type. Also,influenced by the neutral leads 13 are the separate current transformersindicated at 18 which are provided for supervisory, protective andinstrumentation purposes and have no connection with the presentinvention.

The internal excitation transformer 15 has a second primary winding 19which is supplied by a supplementary phase-selectable power source. InFIG. 1 (as well as FIGS. 4, Sand 6), this takes the form of asupplementary multiphase winding 20 in the stator bore, preferably aliquid cooled winding disposed in the slots of the dynamoelectricmachine stator along with the main winding and having only one-half turnfor each phase. Each phase conductor such as 20a of the supplementarywinding is placed in the proper slot to give the desired phaserelationship with respect to a phase winding such as 11a of the mainwinding. This phase relationship is determined by the slot in whichphase winding 20a is placed (cf. FIG. 3, reference number 40). Theoutput from each of the phases such as 20a of the supplementary windingis supplied through a corresponding winding such as 19a of the exciterprimary winding 19 and a reactor 21a connected in series therewith to aninternal grounded neutral connection 22.

The two primary windings 19a and 16a are operatively disposed on acommon core in the excitation transformer 15 so as to generate voltagein a corresponding phase winding 23a of a delta-connected secondarywinding 23. The output leads from secondary 23 leave the generatorcasing via bushings 24 and are connected as the 3-phase input to therectifier bank 9.

Referring now to FIG. 2 of the drawing, an actual arrangement ofelements in a large generator is shown using the same reference numeralswhere possible to depict identical parts. A cross-sectional view of theupper half at one end of dynamoelectric machine shows the gastightcasing 3 to contain a laminated stato then be recooled-by suitable heatexchangers such as 25located inside the casing.

The main winding 11 is also cooled internally by a liquid coolingsystem, described in more detail in the aforesaid Kilboume patent, whichsupplies a liquid such as deionized water from internal headers 26through insulated hoses 27 to liquid cooled bar terminations 28, andthence through hollow winds to'be cooled and recirculated at the otherend of the generator. The line leads (not shown) from main winding 11are brought out of the lower part of the generator through high-voltagebushings.

In accordance with the preferred form of the present invention, theneutral leads 13 are extended into the upper portion of the generator.Casing 3 is enlarged by providing a dome 3a which is adapted by means ofsuitable conduits 29 to be cooled by gas recirculating over the heatexchanger 25 and recirculating through the dome 3a to cool thecomponents therein. The components include the internal excitationtransformer 15,

reactors 21 with neutral connection 22 and the main winding neutralconnection 17, led through the casing by means of bushing 17a toexternally mounted conventional grounding and protective relayingequipment 17b.

The excitation transformer 15 includes three laminated cores such as 30,one for each phase, arranged in a staggered configuration along the topof the dynamoelectric machine inside dome 3a. Each of the cores isarranged to provide flux linkage paths between a pair of primarywindings such as 16a and 19a and a secondary winding. such as 23a. Theprimary winding 160 comprises a single turn primary formed by anL-shaped hollow conductor 31 which has a vertical leg passing throughthe transformer core 30. The upper end of the hollow conductor 31 isconnected at the neutral connection 17. with two other similarconductors from the other two phases and held in a bracket 32, afterfirst passing through the supervisory current transformers 18.

The lower end of hollow conductor 31 is electrically connected to one ofthe neutral ends of the phase windings by means of a flexible electricalconnection 33. A hollow insulating sleeve 34 in communication with coldgas supplypipe 35 and also with the interior of conductor 31 provides aflow of cooling gas as shown by the arrows from the heat exchanger 25through the conductor 31 to an outlet opening 36 at the neutral point.Cooling ducts 30a located between the packages of laminated iron intransformer cores 30 are similarly connected by baffles (not shown) tocommunicate with cold gas supply pipe 35. Thus, both the exteriors ofthe cores and windings located in dome 30, as well as the interior ofthe neutral lead primary winding and the excitation transformer coresare cooled by the generator cooling gas.

As mentioned previously in connection with FIG. 1, the phase-selectablepower source for the other primary winding 19 of the internal excitationtransformer is a supplementary winding disposed in the slots of thedynamoelectric machine along with the main winding. Reference to FIG. 3of the drawing will show a cross section through the dynamoelectricmachines slots. The slots contain insulated armature bars 36 held inplace by insulated dovetail wedge members 37. At

three equally spaced locations around the bore of the armature core, aspecially adapted wedge member 38 supports an insulated conductor member40 composed of hollow ducts and solid strands and extends the length ofthe generator core and is adapted tolink with the synchronous rotorfield flux. Conductor 40 thereby forms a one-half turn phase windingrepresented by phase winding 20a in FIG. 1.

The three conductors 40 are connected together with a suitable neutralconnection at one end of the generator stator, whereas at the other end,they are led out of the slot and carried within an insulating sheath, asindicated by reference numeral 41 in FIG. 2 to connect with the primarywinding 19a. The other end of primary winding 19a is led via aninsulated hollow conductor 42 to the reactor winding 21a and thence viaa similar hollow lead 43 to the neutral connection 22.

The neutral connection 22 is in the form of a hollow liquid headerconnected by a hose member 44 to a liquid coolant supply header 45similar to previously mentioned liquid header 26.

In the manner described above, an electrical series connection isthereby provided from a phase winding 20a (disposed in the top of astator slot) through excitation primary winding 19a and reactor winding21a to the neutral connection 22, a similar arrangement being providedfor each of the three phases. Also means for liquid cooling the abovearrangement includes the hose connection 44 to the series connectedwindings 21a, 19a, 200 which are in fluid communication with oneanother.

OPERATION First, from a standpoint of functioning of the disclosedelectrical circuitry, the primary winding 16 of the internal excitationtransformer is responsive to current flowing through the neutral leads13 to and from the internal neutral connection 17. Thus, primary winding16 represents the current transformer or CT of more conventional staticexcitation systems.

The supplementary winding 20 is responsive to air gap or synchronousflux produced by the rotating field winding 7, and supplies the otherprimary winding 19 of the internal excitation transformer. Since therotor synchronous flux generates a virtual voltage in the main statorwinding which equals the generator terminal voltage if no stator loadcurrent is flowing and which differs from the generator terminal voltageby the stator leakage reactance voltage drop if stator current isflowing, the primary winding 19 is therefore somewhat analogous to thepotential transformer or PT winding of previous static excitationsystems. However, it is proportional to generator virtual voltage (airgap flux) rather than generator terminal voltage (virtual voltage lessleakage reactance drop),

Another important difference with this system is that, since thesupplementary winding 20 can be placed in any desired set of statorslots, the phase displacement of this excitation winding with respect tothe main winding can be freely selected to give the optimum compoundingrelations between the current and potential primary windings on theexcitation transformer simply by selecting the proper set of slots. Thesupplementary winding thus provides another degree of flexibility notachieved with prior art static excitation systems.

The purpose of the reactors is to stabilize operation of the system overan extremely wide range of generator terminal conditions, both steadystate and transient. By providing relatively high impedance in thiswinding circuit of the 3 winding transformer, the reactors provide astiffer coupling between the current responsive primary winding 16, andthe transformer secondary winding 23.

Primary windings 16, 19 together create flux linking with the secondarywinds 23 supplying the rectifier bank 9. Thus a rectified DC fieldcurrent is supplied to the rotor slip rings. 8 which is responsive bothto generator current and generator potential in a wellknown compoundingeffect which can be designed to produce an instantaneous excitationforcing action and a steady state self-regulating action which minimizesgenerator response time and reduces control requirements.

From a standpoint of the physical arrangement, the excitationtransformer 15 with windings 16, 19, 23 is physically smaller than priorexcitation transformers by virtue of being effectively cooled by thegenerator cooling systems, both gas and liquid in the presentembodiment. Since it is much smaller in size than conventional externalexcitation transformers, it becomes practical to locate the excitationtransformer internally so that it thereby becomes practical to use thegenerator cooling system and to integrate into the structure of theinternal generator neutral leads. Thus a synergistic effect is achievedby locating the internal excitation transformer within or in closeproximity to the generator casing so as to utilize the generator coolingsystem.

By connecting the neutral ends of the phases internally rather thancarrying them out through neutral bushings, a very compact andconvenient arrangement is achieved. The location of the neutralconnections at the top of the generator while the line ends of thephases are brought out at the bottom makes it physically very simple torun the neutral leads through the internal excitation transformer coresproviding onetum primaries. At the same time this provides the maximumin accessability for installation or servicing of the excitationtransformers (by removing dome 3a), and frees space at bottom of thegenerator so that the isolated phase bus connections can be made in theeasiest possible way. By locating the generator grounding transformerprotective relaying equipment 17b outside the generator casing but inclose proximity to the neutral point, the maximum in accessibility,protection, and conventional practice in these latter elements isachieved.

Dielectric requirements and duty on this static excitation arrangementare minimized because the excitation transformer couples the neutral endof the generator phase windings rather than the line ends of the phases,and because the potential winding is electrically isolated from the mainwindings.

OF THE INVENTION (FIGS.

MODIFIED FORMS neutral connection 50 is made outside of the generatorcasing after the neutral leads 13 have been brought out through thecasing 3 via bushings 51, first having been brought through theexcitation transformer 15. In this arrangement, the supervisory currenttransformers 18 are also more conveniently located outside of the casingto be accessible for servicing.

In FIG. 5, a slightly different control scheme is employed for theinternal excitation transformer. The silicon controlled rectifiers 10 ofFIG. 1 are eliminated and in their place, an additional control winding52 is added to the internal excitation transformer core. A conventionalvoltage regulator 53 provides a regulated DC voltage which is applied tothe control winding 52. Winding 52 is arranged with respect to the otherwindings so as to enable saturation of the internal excitationtransformer cores and thereby control the output from the secondary.winding 23 to a B-phase diode bridge rectifier bank 9a.

The operation of the foregoing modified form of the invention in FIG. 5is similar to that of a conventional saturable current-potentialtransformer or SCPT with the important difference that it is moreflexible with respect to selection of phase displacement of thesupplementary winding in the slots and also it has a higher response dueto the construction and small size of the internal excitationtransformer.

FIG. 6 is another modification of the invention, representing a slightlydifferent physical arrangement of the generator. The generator casing 3is modified by enclosing the excitation transformer 15 and the reactors21 in a sealed enclosure 55 which is separate from but physicallyclosely adjacent to the generator casing 3. Cooling of the enclosure 55is provided by means of the generator cooling system via communicatingconduits symbolically indicated at 56 and a recirculating arrangement.symbolically shown at 57. The neutral connection 50 is made outside ofthe generator casing as indicated previously in connection with the FIG.4 embodiment.

The physical significance of providing an enclosure which is separate,but located close enough to utilize the dynamoelectric machine coolingsystem can be appreciated by review of the physical arrangement in FIG.2. There the supplementary dome 3a would be replaced by a separatecasing which may yet be located in approximately the same position ontop of the generator. Therefore, the generator design would not be soclosely dependent upon the design of the internal excitation transformerand other components with the exception of the interconnected coolingpassages. Similarly, the enclosure 55 can be located directly beneaththe dynamoelectric machine but closely adjacent thereto.

FIG. 7 illustrates an alternate arrangementfor the supplementaryphase-selectable power source to the primary winding 19 of the internalexcitation transformer. Instead of employing the supplementary winding20 in the main winding slots shown in FIGS. l-6 as a source, aphase-shifting transformer 100 may be used. Transformer 100 has aprimary winding 100d connected to the stator line terminals, and asecondary winding 100b arranged to provide a selected phase shift fromthe generator terminal voltage. In this way a comparable effect isachieved to that of proper slot selection for the aforementionedsupplementary winding 20. The output leads from the secondary 100b ofthe phase-shifting transformer are led into the casing through bushings102 and connected to primary winding 19. Thus optimum compoundingrelationships maybe achieved while still integrating the remainder ofthe elements such as the internal excitation transformer, the generatorneutral leads and the generator cooling system. 7

The transformer 100 may either be located below the generator casingclose to the high voltage bushings 14 as shown, or it can be placedinside the casing similar to the internal excitation transformer inorder to more effectively utilize the generator cooling system. In thelatter case, the connection of the primary winding 100a to the line sideof main winding 1 1 would also be inside the generator casing, and couldeven be connected to taps at some intermediate point in main winding 11if this were desirable.

The operation of FIG. 7 is the same as previously described inconnection with F IG. 1. The phase-shifting transformer 100'isresponsive to synchronous flux provided by the field winding andtherefore a comparable power source to the supplementary windings 20shown in FIGS. 1-6. Optimum compounding is achievable by proper designof the phase-shiftable power source to the primary winding 19 f theinternal excitation transformer.

ADVANTAGES The foregoing arrangements, first of all, have the advantagesinherent in all static excitation systems in that the normal rotatingequipment associated with the separate exciter is eliminated and the endof the generator is free except for the slip rings. Considerable floorspace is saved and separate foundations are eliminated by location ofthe excitation transformers internally. Maximum freedom for thegenerator isolated phase bus is obtained by locating the generatorneutrals and excitation equipment on top of the generator. This providesmaximum accessability and permits the stator frame to be strengthened inits end sections. High response of excitationis provided due to theinherent self-regulating action and the laminated lowtime-constantmagnetic structure of the internal excitation transformers. An optimumcombination of excitation forcing action during system transients andsteady state self-regulating action over an extremely wide range ofgenerator operating conditions can be obtained with minimum controlpower because of the greater flexibility available in selectingcompounding relationships with this system. Location of the excitationtransformer inside the generator casing and employing the neutral leadsof the main winds avoids the necessity for breaking into the isolatedphase bus on the high voltage end of the main windings. Use of thegenerator coolantsgreatly reduces the size of the excitation transformeropposed to conventional external tion system for large internally cooleddynamoelectric machines.

While there is shown what is considered at present to be the preferredembodiment of the invention, it is of course understood that variousother modifications may be made therein. For example, the neutralconnections could be arranged in an enlarged terminal box below thegenerator adjacent to the high voltage bushings. It is intended to coverin the appended claims all such modifications as fall within the truespirit and scope of the invention.

What is claimed is:

1. In a dynamoelectric machine having a rotating field winding, anelectromagnetic stator core and a multiphase set of main armaturewindings, each phase of said main winding having two internal leads,said dynamoelectric machine further having a closed casing and a coolingsystem arranged to recirculate coolant fluids over said windings andcore, the combination of:

an excitation transformer disposed closely adjacent the dynamoelectricmachine core and adapted to be cooled by the dynamoelectric machinecooling system, said transformer having a core, at least two primarywindings and a secondary winding which are disposed in heat exchangerelationship with said dynamoelectric machine coolant fluids,

one of said primary windings consisting of selected internal leads fromsaid main winding of the dynamoelectric machine, and

a supplementary power source connected to the other primary winding ofsaid excitation transformer.

2. The combination according to claim 1, further including rectifiermeans connected to the secondary winding of said excitation transformerand output leads connected to supplyv excitation power to said rotatingfield winding.

3. The combination according to claim 1 wherein said supplementary powersource is a supplementary multiphase winding disposed to link with thesynchronous flux provided by said dynamoelectric machine rotor winding.

4. The combination according to claim 3, wherein said supplementarywinding comprises a set of liquidcooled conductors disposed in slots ofthe dynamoelectric machine core.

5. The combination according to claim 1 wherein said supplementary powersource is a supplementary multiphase transformer connected so as to drawpower from the dynamoelectric machine main armature windings.

6. The combination according to claim 1, wherein said selected leadscomprise the neutral leads of a wyeconnected main winding and whereinsaid leads are connected together inside the dynamoelectric machinecasing along with said excitation transformer so as to comprise acompletely internal static excitation system.

7. The combination according to claim 1, wherein said selected leadscomprise the neutral leads, and wherein said neutral leads pass throughsaid excitation transformer and leave the dynamoelectric machine casingthrough bushings to be connected together in an external neutralconnection.

8. The combination according to claim 1, wherein said selected leadscomprise the internal line leads of said main windings.

9. The combination according to claim 1, wherein at least one portion ofsaid excitation transformer is directly cooled by a fluid coolant whichalso serves to cool the dynamoelectric machine main windings.

10. The combination according to claim 9, wherein said coolant is liquidpumped by said dynamoelectric machine cooling system through both themain winding and at least one of said excitation transformer windings.

11. The combination according to claim 1, wherein at least one portionof said excitation transformer is cooled by fluid coolant which alsoserves to cool the core of the dynamoelectric machine.

v 12. The combination according toclaim l 1, wherein said coolant is gascirculated by said dynamoelectric machine cooling system over both thedynamoelectric machine core and the core of said excitation transformer.

13. The combination according to claim 1, wherein said excitationtransformer is disposed in a dome attached to said dynamoelectricmachine casing and opening into said casing.

14. The combination according to-claim 1, wherein said excitationtransformer is disposed in a first enclosure, said dynamoelectricmachine casing comprises a second enclosure, and further includingconduit means connecting said enclosures and having means to conductfluid coolant between said enclosures.

1. In a dynamoelectric machine having a rotating field winding, anelectromagnetic stator core and a multiphase set of main armaturewindings, each phase of said main winding having two internal leads,said dynamoelectric machine further having a closed casing and a coolingsystem arranged to recirculate coolant fLuids over said windings andcore, the combination of: an excitation transformer disposed closelyadjacent the dynamoelectric machine core and adapted to be cooled by thedynamoelectric machine cooling system, said transformer having a core,at least two primary windings and a secondary winding which are disposedin heat exchange relationship with said dynamoelectric machine coolantfluids, one of said primary windings consisting of selected internalleads from said main winding of the dynamoelectric machine, and asupplementary power source connected to the other primary winding ofsaid excitation transformer.
 2. The combination according to claim 1,further including rectifier means connected to the secondary winding ofsaid excitation transformer and output leads connected to supplyexcitation power to said rotating field winding.
 3. The combinationaccording to claim 1 wherein said supplementary power source is asupplementary multiphase winding disposed to link with the synchronousflux provided by said dynamoelectric machine rotor winding.
 4. Thecombination according to claim 3, wherein said supplementary windingcomprises a set of liquid-cooled conductors disposed in slots of thedynamoelectric machine core.
 5. The combination according to claim 1wherein said supplementary power source is a supplementary multiphasetransformer connected so as to draw power from the dynamoelectricmachine main armature windings.
 6. The combination according to claim 1,wherein said selected leads comprise the neutral leads of awye-connected main winding and wherein said leads are connected togetherinside the dynamoelectric machine casing along with said excitationtransformer so as to comprise a completely internal static excitationsystem.
 7. The combination according to claim 1, wherein said selectedleads comprise the neutral leads, and wherein said neutral leads passthrough said excitation transformer and leave the dynamoelectric machinecasing through bushings to be connected together in an external neutralconnection.
 8. The combination according to claim 1, wherein saidselected leads comprise the internal line leads of said main windings.9. The combination according to claim 1, wherein at least one portion ofsaid excitation transformer is directly cooled by a fluid coolant whichalso serves to cool the dynamoelectric machine main windings.
 10. Thecombination according to claim 9, wherein said coolant is liquid pumpedby said dynamoelectric machine cooling system through both the mainwinding and at least one of said excitation transformer windings. 11.The combination according to claim 1, wherein at least one portion ofsaid excitation transformer is cooled by fluid coolant which also servesto cool the core of the dynamoelectric machine.
 12. The combinationaccording to claim 11, wherein said coolant is gas circulated by saiddynamoelectric machine cooling system over both the dynamoelectricmachine core and the core of said excitation transformer.
 13. Thecombination according to claim 1, wherein said excitation transformer isdisposed in a dome attached to said dynamoelectric machine casing andopening into said casing.
 14. The combination according to claim 1,wherein said excitation transformer is disposed in a first enclosure,said dynamoelectric machine casing comprises a second enclosure, andfurther including conduit means connecting said enclosures and havingmeans to conduct fluid coolant between said enclosures.